Cal. Code of Civil Procedure § 2034.210

After the setting of the initial trial date for the action, any party may obtain discovery by demanding that all parties simultaneously exchange information concerning each other’s expert trial witnesses to the following extent: (a) Any party may demand a mutual and simultaneous exchange by all parties of a list containing the name and address of any natural person, including one who is a party, whose oral or deposition testimony in the form of an expert opinion any party expects to offer in evidence at the trial. (b) If any expert designated by a party under subdivision (a) is a party or an employee of a party, or has been retained by a party for the purpose of forming and expressing an opinion in anticipation of the litigation or in preparation for the trial of the action, the designation of that witness shall include or be accompanied by an expert witness declaration under Section 2034.260. (c) Any party may also include a demand for the mutual and simultaneous production for inspection and copying of all discoverable reports and writings, if any, made by any expert described in subdivision (b) in the course of preparing that expert’s opinion.